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1.3.4 Conversion     For those wishing to ease themselves into working with metric gears

by looking at them in terms of familiar inch gearing relationships and mathematics, Table 1-5 is offered as a means to make a quick comparison.

Table 1-5 Spur Gear Design Formulas

To Obtain From Known Use This Formula* Pitch Diameter Module D = mN Circular Pitch Module Pc = mp = D p                 N    Module  Diametral Pitch m = 25.4           Pd Number of Teeth Module and Pitch Diameter N = D       m Addendum Module a = m Dedendum Module b = 1.25m Outside Diameter Module and Pitch Diameter or Number of Teeth Do = D + 2m = m (N + 2) Root Diameter Pitch Diameter and Module DR= D - 2.5m Base Circle Diameter Pitch Diameter and Pressure Angle Db = D cos f   Base Pitch  Module and Pressure Angle Pb = m p cos f Tooth Thickness at Standard Pitch Diameter Module Tstd =   p  m            2  Center Distance Module and Number of Teeth C = m (N1 + N2)               2  Contact Ratio Outside Radii, Base Circle Radii Center Distance, Pressure Angle mp=(1Ro-1Rb)½+(2Ro-2Rb)½-Csinf                  m p cos f Backlash (linear)  Change in Center Distance B = 2(DC)tan f Backlash (linear)  Change in Tooth Thickness B = DT Backlash (linear) Along Line-of-action  Linear Backlash Along Pitch Circle BLA = B cos f Backlash, Angular  Linear Backlash aB = 6880 B (arc minutes)                 D       Mm. No. of Teeth for No Undercutting Pressure Angle Nc =   2            sin²f

* All linear dimensions in millimeters    Symbols per Table 1-4

SECTION 2    INTRODUCTION TO GEAR TECHNOLOGY This section presents a technical coverage of gear fundamentals. It is intended as a broad coverage written in a manner that is easy to follow and to understand by anyone interested in knowing how gear systems function. Since gearing involves specialty components, it is expected that not all designers and engineers possess or have been exposed to every aspect of this subject. However, for proper use of gear components and design of gear systems it is essential to have a minimum understanding of gear basics and a reference source for details.    For those to whom this is their first encounter with gear component it is suggested this technical treatise be read in the order presented so as to obtain a logical development of the subject. Subsequently, and for those already familiar with gears, this material can be used selectively in random access as a design reference.

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